Air Regulator and Brake Issues

[MajesticSyntax]

I have been struggling to diagnose my brake issues since the Oklahoma get together in October. My brakes would slowly seize up the longer my truck was running. I have bled brakes, checked the drums, all that jazz. All of it was fine. I think I have finally figured out what the problem is, but I have no idea how to fix it.

When I got the truck the max pressure of the air lines was regulated to 120. Recently I have learned the the regulator has not been shutting off at that pressure and instead, over pressurizing and eventually locking my brakes. I am upset that I did not see that sooner, but now here's my problem. I took the air pressure regulator apart and cleaned it up and reinstalled it. Now when my truck reaches it's new max pressure of 95 psi it just starts popping off excess air instead of shutting off the compressor. Occasionally the compressor will shut off like it's supposed to, but more often than not, it just blows off the excess air. My question is this: What so I need to do to fix this? The regulator is a really simple device and I'm not sure how it could be repaired, so does that mean my issues lie in the compressor itself? Any information would be greatly appreciated.

CEM

 

[gimpyrobb]

Untill you started talking about the air pressure, it sounded like the airpack needed rebuilt. I don't know about the air compressor goveners.

 

[MajesticSyntax]

Untill you started talking about the air pressure, it sounded like the airpack needed rebuilt. I don't know about the air compressor goveners.

Yeah, I looked into that already, but all is well in the braking department. Thank you for the help though.

 

[gringeltaube]

................................
My brakes would slowly seize up the longer my truck was running. I have bled brakes, checked the drums, all that jazz. All of it was fine..................
CEM

If all 6 drums get hot there might be a problem with the master cylinder not allowing fluid to return. Check brake pedal adjustment, return spring, swollen rubber cup, etc.
This has nothing to do with the air governor - which also needs to be re-adjusted.
Read here http://www.steelsoldiers.com/deuce/36059-air-governor-questions-2.html


G.

 

[MajesticSyntax]

If all 6 drums get hot there might be a problem with the master cylinder not allowing fluid to return. Check brake pedal adjustment, return spring, swollen rubber cup, etc.
This has nothing to do with the air governor - which also needs to be re-adjusted.
Read here http://www.steelsoldiers.com/deuce/36059-air-governor-questions-2.html


G.

I understand what you are saying, but my brake problems have been resolved now that my air pressure has been regulated. The problem lies in how it is being regulated. Instead of kicking open and closed like it should when the air line pressure drops, the regulator just blows off the excess air over and over with this popping sound, usually more than once or twice a second. I think before it was just stuck in 'open' and it was over pressurizing the entire system. Now that it is capping at 95 psi... it's just not ever closing off the system...

 

[Bill W]

CEM
I vaguely remember reading something on this in the past so take it for what its worth, when the air govenor reaches its preset pressure it trips a valve/switch on top of the compressor and puts it into bypass mode and it sounds like thats whats (Not) happening now, as mentioned the air gov is pretty simple I think you also need to go look at the compressor

 

[Barrman]

The "unloader valve" is what the small line from the regulator to the compressor controls. It is basically just a spring behind a flat piece of metal that opens and closes with air pressure. Depending on which style of compressor you have, they are either real easy to get to or a pain. This valve is what turns the compressor "on or off" even though the compressor really keeps running all the time.

Having written that. I think you have other problems. The pop off valve on the air tanks should open around 120-130 depending on the individual valve. If yours is now opening at 95, then it is bad.

The brakes on a M35 are hydraulic. You have a master cylinder and wheel cylinders just like most normal sized vehicles have had for the past 80 years.

The system needs to be able to breathe. That is why there is a vent on the master cap. Blow air through it just to verify it will breathe. Although, non venting normally leaves a vehicle with no brakes over time. I mentioned it just in case.

Pushing the pedal pushes a a rod which pushes piston inside the mc. That piston pushes fluid through the lines and hoses to the wheel cylinders. They then move pushing the brake shoes against the drums causing friction which slows down the truck. When you let go of the pedal, springs on the shoes pull them back. This causes the fluid to travel back to the master cylinder resevoir. A little bit of dirt/rust/crud in the port at the bottom of the resovoir could cause the fluid to not be able to return. no fluid return means residual pressure in the system which keeps your shoes in contact with the drums causing excess heat build up. All of this happens with or without the air pack doing a thing or having air in it. A pedal rod adjusted with not enough free play will do the same thing. How much free play do you have when you push the pedal before you get resistance? 1-1/2"-2" is what it should be.

The air pack is just another piston to help push the fluid toward the wheel cylinders. The airpack has a little piston/valve inside that gets pushed by the brake fluid when you push the pedal. That valve lets air get to the back of the pack where the air pushes against a huge 4" piston. That piston is attached to a smaller piston that then pushes the brake fluid harder toward the wheel cylinders.

A small amount of residual pressure in the hydraulic system will allow a small amount of air to "help" push all the time. You lowering the operating pressure by 30 psi just changed how much the pack is "helping" all the time. At least that is how I read this because with everything working right the air pressure doesn't matter if your foot is off the pedal.

I think you have either a clogged up compensating port in your mc, not enough free play or a bad air pack valve body. Spend $75 and get a kit for both the master and the air pack. Read the -30 and -20 manuals and do a rebuild of both after you have cleaned them both within an inch of their lives. Refill with BFS and drive happy.

I hope this helps. Not trying to pick on you, just point out that I don't think you found the problem yet. Mearly hid it better. Oh, one more thing. With the system aired up and the engine off. Push the pedal and let go. Do you hear a Pssst up around the engine air filter? Or do you hear the psssst all the time from up there? Air all the time indicates a bad air pack valve body. The valve body in my Gasser M35 got so bad that it was blowing the oil out of the oil bath air filter any time there was air in the system.

 

[MajesticSyntax]

The "unloader valve" is what the small line from the regulator to the compressor controls. It is basically just a spring behind a flat piece of metal that opens and closes with air pressure. Depending on which style of compressor you have, they are either real easy to get to or a pain. This valve is what turns the compressor "on or off" even though the compressor really keeps running all the time.

Having written that. I think you have other problems. The pop off valve on the air tanks should open around 120-130 depending on the individual valve. If yours is now opening at 95, then it is bad.

The brakes on a M35 are hydraulic. You have a master cylinder and wheel cylinders just like most normal sized vehicles have had for the past 80 years.

The system needs to be able to breathe. That is why there is a vent on the master cap. Blow air through it just to verify it will breathe. Although, non venting normally leaves a vehicle with no brakes over time. I mentioned it just in case.

Pushing the pedal pushes a a rod which pushes piston inside the mc. That piston pushes fluid through the lines and hoses to the wheel cylinders. They then move pushing the brake shoes against the drums causing friction which slows down the truck. When you let go of the pedal, springs on the shoes pull them back. This causes the fluid to travel back to the master cylinder resevoir. A little bit of dirt/rust/crud in the port at the bottom of the resovoir could cause the fluid to not be able to return. no fluid return means residual pressure in the system which keeps your shoes in contact with the drums causing excess heat build up. All of this happens with or without the air pack doing a thing or having air in it. A pedal rod adjusted with not enough free play will do the same thing. How much free play do you have when you push the pedal before you get resistance? 1-1/2"-2" is what it should be.

The air pack is just another piston to help push the fluid toward the wheel cylinders. The airpack has a little piston/valve inside that gets pushed by the brake fluid when you push the pedal. That valve lets air get to the back of the pack where the air pushes against a huge 4" piston. That piston is attached to a smaller piston that then pushes the brake fluid harder toward the wheel cylinders.

A small amount of residual pressure in the hydraulic system will allow a small amount of air to "help" push all the time. You lowering the operating pressure by 30 psi just changed how much the pack is "helping" all the time. At least that is how I read this because with everything working right the air pressure doesn't matter if your foot is off the pedal.

I think you have either a clogged up compensating port in your mc, not enough free play or a bad air pack valve body. Spend $75 and get a kit for both the master and the air pack. Read the -30 and -20 manuals and do a rebuild of both after you have cleaned them both within an inch of their lives. Refill with BFS and drive happy.

I hope this helps. Not trying to pick on you, just point out that I don't think you found the problem yet. Mearly hid it better. Oh, one more thing. With the system aired up and the engine off. Push the pedal and let go. Do you hear a Pssst up around the engine air filter? Or do you hear the psssst all the time from up there? Air all the time indicates a bad air pack valve body. The valve body in my Gasser M35 got so bad that it was blowing the oil out of the oil bath air filter any time there was air in the system.

I greatly appreciate the advice you have given I will look into those things much more closely. The only reason the pressure was dropped to 95 was so I could see if it ended up climbing higher (via the pressure gauge) due to the regulator malfunctioning again. As it was at 120 psi, if it climbed any higher it would simply peg out and I could not see any change in pressure from that perspective. I intentionally adjusted the pressure to 95, it was not an accident or coincidence, but I made certain to stay within the TM guidelines.

As of now, the brakes seem to be completely fine, but I will look into these things. As far as brake 'slack' I have a little less than 2 inches of play once everything is aired up. And when I push on the pedal it only hisses for a short, short time. When I bled the brakes and checked the MC originally, everything was nice and clean, but I have a question regarding the vent line. Where is it supposed to connect once it leaves the MC?

 

[rlwm211]

I had an issue with my deuce last summer. I was travelling back to my residence after a long weekend and my brakes gradually came on over a distance of about 12 miles. I found the master cylinder was not returning the piston to the "released" position. I ended up stranded on the side of the road, all 6 brake sets locked tight. Fortunately for me, I was within about 4 miles of my house and all back country roads to get home. I cracked the brake line at the master and could hear all of the brakes releasing as the pressure backed off. I drove home slowly, with a follow car and managed to get home without using the brakes. When I pulled the master to rebuild it, it was "NASTY" inside. I rebuilt the MC and all has been well since.

When I bought my truck, it had a bad wheel cylinder and the truck was dry as far as brake fluid goes. I figure the master got rusted up while empty when the truck was sitting in the motor pool. I had already fixed the wheel cylinder and had thought all was well once the brakes were bled out. I am planning on rebuilding the airpack in the spring, and also pulling all the wheels and hubs to grease the bearings. I figure that if I finish redoing the brake system I will be set for many years.

As to your air problem, the unloader is the key to set the system pressure. If you have not already, go to the forums and in the section marked the deuce, there is a F.A.Q. and in there are all of the manuals for the deuce and you will find out how to deal with your air pressure problem there.

Good luck

Just my two cents

RL

 

[Wolf.Dose]

I love this thematics, for they not so very difficult to solve when you know something about brake systems.
First: The brake system in question is a so called air over hydraulic system.
Second: The max. air pressure for this system should be at 120 psi, for this is the designe pressure, the regulator / govenerer for this must switch between 90 and 120 PSI.
Third: Theoretically it is impossible that the brake drags when the brake pedal is not pushed. The master cylinder has no information hydraulicaly, that a braking is required.
Fourth: The air is just a help to reduce the pedal force.
What is the summery of that: The pedal free travel is to small, so the air alway puts some pressure on the air assistance due to some remaining hydraulic pressure; or the free travel of the brake shoes is to tight.
The only advice between all try and error: Set the brakes to factory standard so they must work accordingly!
Some of you might cry loud about this, but try it out, it will work. Brakes are just a friction device and need to be treated according the physiacl laws.
Thats it.
Wolf

 

[rlwm211]

First: The Brake system is NOT an Air over Hydraulic. It is an Air assisted hydraulic system. The only difference between this system and a vacuum or hydraulically boosted system is the fact that it uses air to assist braking effort. An M105 trailer uses an Air over hydraulic system. There is a big difference between the two as to how the brakes are applied.

Second: The air pressure on the system will not by itself cause a brake application unless there is a problem in the air pack.

Third: Perhaps you did not read my post, but I found that the bore for the piston was so corroded and fouled the piston could not return to the "released" position.

Fourth: You fourth point is correct.

Your summary is wrong in that the master cylinder must release all pressure so that the piston can allow fluid to return, or be replenished by the resevoir is it is needed. If pressure is always kept on the system, then the piston cannot access the resevoir.

There are most likely two issues in this situation and the easiest way to deal with them is to follow the diagnostic procedures for each one individually.

Just my Two cents

RL

 

[tm america]

i agree fully with rlwm211 and it is very possible and common to have more than one problem with a brake system.brakes should always be serviced as a system from top to bottom they need to be correct or you will have problems .maybe not today but it will happen .that being said if you see rust in a wheel cylinder you should go through the whole hydraulic system.this is the difference between knowing you will have brakes or hoping you will.
make sure your air system is working right first since it sounds like you have a regulation problem then look at your airpak to see what got damaged from having to much air pressure.a leaking seal in the airpak will cause the brakes to on

 

[Bill W]

my brakes would build pressure when driving do to a weak brake return spring allowing the push rod to put slight pressure on the M/C . When the truck wasn't moving the pedal stayed where it was suppose to but the spring was weak enough to let the pedal move when the truck would bounce some going down the road kind of like lightly pumping the pedal...go figure